The invention relates to radiographic apparatus of the kind arranged to provide a representation of the variation of absorption with position across a planar (or substantially planar) slice of a body with respect to penetrating radiation.
In U.S. Pat. No. 3,946,234 there is described an apparatus for that purpose which includes a source of penetrating radiation arranged to provide a fan-shaped spread of radiation lying in the plane of the slice. Suitable collimators are provided to define a plurality of pencil beams from that spread, and an array of detectors is arranged to measure the intensity of each of those beams after passage through the body. The detectors are required to provide output signals indicative of the absorption suffered by the radiation over a large number of paths through the body. For that purpose the source and detectors are reciprocated in the plane of the slice and orbited about a common axis normal to that plane. The output signals are processed by any suitable method, for example the convolution method described in U.S. Pat. No. 3,924,129, to provide the desired representation.
Further developments of the apparatus are described in U.S. Pat. No. 3,937,963 and U.S. Pat. application Ser. No. 544,799, filed on Jan. 28, 1975. According to those specifications, the fan-shaped spread of radiation subtends an angle sufficient to include the whole region of interest in then plane of the slice so that a complete scan can be effected solely by orbiting the source and detectors about the common axis.
It is an object of the present invention to provide an alternative apparatus for the purpose of providing a similar representation of the variation of absorption with position across a planar (or substantially planar) slice of a body with respect to penetrating radiation.
According to the invention there is provided apparatus for examining a body by means of penetrating radiation including means for generating output signals, representative of the absorption suffered by the radiation in passage along respective beam paths through a region of the body, for processing to provide a representation of the distribution of absorption of the radiation in the region, and combining means for combining groups of output signals relating to groups of beam paths, chosen so that the beam paths of a group pass through a common elemental area of the region from different directions, to provide composite output signals representing the absorption of the radiation in passage through the body along composite beam paths, which are narrower in the vicinity of the respective elemental areas than in other parts of the region, so that the said processing can be effected on a plurality of output signals including at least some of said composite output signals.